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Cc: php-i18n@lists.php.net
Date: Thu, 2 Feb 2006 16:45:39 -0800
To: PHP Developers Mailing List <internals@lists.php.net>
Subject: Unicode string iterator performance
From: andrei@gravitonic.com (Andrei Zmievski)

You probably saw that I have committed initial implementation of=20
TextIterator. The impetus for this is that direct indexing of Unicode=20
strings via [] operator is slow, very slow, at least currently. The=20
reason is that [] cannot simply perform random-offset indexing into=20
UCHar* strings. It needs to start from the beginning of the string and=20=

iterate forward until it reaches the desired offset, because our=20
default unit is a codepoint, which can take up 1 or 2 UChar's.

So here are some (rough) numbers on the relative performance of=20
TextIterator vs. []. The script I used was a simple one (attached after=20=

the signature). Each test was 10000 runs over 500-character string.

[] operator:  27.16373 s
TextIterator: 1.89697 s (!)

For comparison, running the same [] operator test on a 500-character=20
binary (old-style) string gives me 9.11334 s. Quite interesting, I'd=20
say.

I am not sure how we can optimize [] to be faster than the iterator=20
approach. Food for thought?

- Andrei

<?php
$a =3D str_repeat('a\U010201bc=DF', 100);
var_dump($a);

/* warm up the engine */
for ($x =3D 0; $x < 100; $x++) {
foreach (new TextIterator($a) as $c) {
}
}

/* measure [] */
$start =3D microtime(true);
for ($x =3D 0; $x < 10000; $x++) {
     $len =3D strlen($a);
     for ($i =3D 0; $i < $len; $i++) {
         $c =3D $a[$i];
     }
}
$end =3D microtime(true);

printf("[] run time: %.5f\n", $end - $start);

/* measure iterator */
$start =3D microtime(true);
for ($x =3D 0; $x < 10000; $x++) {
foreach (new TextIterator($a) as $c) {
}
}
$end =3D microtime(true);

printf("iterator run time: %.5f\n", $end - $start);
?>